Turbocharger wheel with sound control

ABSTRACT

A turbocharger turbine wheel includes a hub and a plurality of blades. Both the center of mass of the hub and the center of mass of the plurality of blades are on an axis of rotation. The blades are circumferentially spaced such that they are rotationally asymmetric. Each consecutive pair of blades is characterized by a spacing angle. A line that intersects with and is normal to the axis of rotation defines a plane of symmetry, and the spacing angles are symmetric across the plane of symmetry.

The present invention relates to a wheel for a turbocharger, and moreparticularly, to an automotive turbocharger wheel having blades spacedat angles that limit the generation of noise in the audible range.

BACKGROUND OF THE INVENTION

Radial automotive turbines are generally configured with an inlet volutein which a stream of exhaust gas spirals in to drive the blades of aturbine wheel. At the location around the volute where the exhauststream first opens up to the turbine wheel, there is a structuralfeature where the blades pass from being in close proximity to thesurrounding volute wall to being distant from the volute wall. Becauseof the appearance of this feature in cross section, it is sometimesreferred to as the tongue.

Automotive turbochargers often have on the order of seven to eighteenturbine blades. Within the lower range of numbers of blades, and attypical turbine rotational rates, the blades may pass the tongue at afrequency that is within the human audible range. This creates a hummingnoise that is not desirable.

One solution to this problem is to increase the number of blades, suchas from eleven to thirteen blades for a smaller automotive turbocharger.This causes the blades to pass the tongue at a frequency that is abovethe human audible range at typical operating speeds. Unfortunately, theincrease in the number of blades can lead to several undesirableconsequences. For example, the increase in blades can lead to a wheelthat is more expensive to make (both because of an increase in materialsand because of an increase in tooling costs). Also, because there isless room for fillets at the base of each blade, the blade support isweakened, leading to a less durable turbine wheel. Moreover, because thewheel will likely have a greater rotational inertia, it will be lessresponsive to changes in the exhaust pressure, such as during enginetransient operating conditions.

There exists a need for durable and cost-efficient turbine wheels thatminimize undesirable noise. Preferred embodiments of the presentinvention satisfy these and other needs, and provide further relatedadvantages.

SUMMARY OF THE INVENTION

In various embodiments, the present invention solves some or all of theneeds mentioned above, providing a durable and cost-efficient turbinewheel that minimizes undesirable noise.

The turbocharger wheel, e.g., a turbine wheel, which is for use as partof a rotor group, includes a hub and a plurality of blades. The turbinewheel is characterized by a line defining an axis of rotation. Both thecenter of mass (“CM”) of the hub and the CM of the plurality of bladesare on the axis of rotation. The plurality of blades iscircumferentially spaced around the hub such that the blades arerotationally asymmetric around the axis of rotation. Advantageously,this asymmetry spreads the acoustic energy generated by the bladespassing the volute tongue over a range of different frequencies, therebyreducing the acoustic energy at any one frequency. This, in turn,provides for automotive turbine wheels to be made with fewer blades thanmight otherwise be desirable for rotationally symmetric blades thatconcentrate acoustic energy in frequencies that are audible to humans.

Each consecutive pair of blades is characterized by a spacing anglebetween the consecutive pair of blades. A set of spacing angles thatmeet all the requirements can be iteratively calculated. In a furtherfeature, the turbocharger wheel, e.g., a turbine wheel is characterizedby a second line that intersects with and is normal to the line definingthe axis of rotation. The line defining the axis of rotation and thesecond line define a plane of symmetry by extending along and beingcontained within the plane, and the spacing angles of the plurality ofblades are symmetric across the plane of symmetry. Advantageously, thisplanar symmetry provides for the angles to be iteratively calculatedusing a significantly reduced number of variables, and therefore areduced number of calculations.

Other features and advantages of the invention will become apparent fromthe following detailed description of the preferred embodiments, takenwith the accompanying drawings, which illustrate, by way of example, theprinciples of the invention. The detailed description of particularpreferred embodiments, as set out below to enable one to build and usean embodiment of the invention, are not intended to limit the enumeratedclaims, but rather, they are intended to serve as particular examples ofthe claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system view of an embodiment of a turbocharged internalcombustion engine under the invention.

FIG. 2 is a cross sectional view of a turbine used in the turbochargedinternal combustion engine depicted in FIG. 1.

FIG. 3 is a depiction of a set of blade spacing angles having a plane ofsymmetry.

FIG. 4 is an embodiment of a method of designing and creatingturbocharger wheel tooling for creating a turbocharger wheel.

FIG. 5 is a depiction of an offset between a center of rotation and a CMof a set of blades.

FIG. 6 is a depiction of a set of blade spacing angles having a plane ofsymmetry and having an odd number of blades.

FIG. 7 is a depiction of a set of blade spacing angles having a plane ofsymmetry and having an even number of blades.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention summarized above and defined by the enumerated claims maybe better understood by referring to the following detailed description,which should be read with the accompanying drawings. This detaileddescription of particular preferred embodiments of the invention, setout below to enable one to build and use particular implementations ofthe invention, is not intended to limit the enumerated claims, butrather, it is intended to provide particular examples of them.

Typical embodiments of the present invention reside in a motor vehicleequipped with an internal combustion engine (“ICE”) and a turbocharger.The turbocharger is equipped with a turbine wheel characterized by aunique blade configuration that provides for durability, a lowrotational moment of inertia, and quiet operation within the human rangeof hearing.

With reference to FIG. 1, a typical embodiment of a turbocharger 101having a radial turbine and a radial compressor includes a turbochargerhousing and a rotor group configured to rotate within the turbochargerhousing around an axis of rotation 103 during turbocharger operation onthrust bearings and two sets of journal bearings (one for eachrespective rotor wheel), or alternatively, other similarly supportivebearings. The turbocharger housing includes a turbine housing 105, acompressor housing 107, and a bearing housing 109 (i.e., a centerhousing that contains the bearings) that connects the turbine housing tothe compressor housing. The rotor group includes a radial turbine wheel111 located substantially within the turbine housing, a radialcompressor wheel 113 located substantially within the compressorhousing, and a shaft 115 extending along the axis of rotation, throughthe bearing housing, to connect the turbine wheel to the compressorwheel.

The turbine housing 105 and turbine wheel 111 form a turbine configuredto circumferentially receive a high-pressure and high-temperatureexhaust gas stream 121 from an engine, e.g., from an exhaust manifold123 of an internal combustion engine 125. The turbine wheel (and thusthe rotor group) is driven in rotation around the axis of rotation 103by the high-pressure and high-temperature exhaust gas stream, whichbecomes a lower-pressure and lower-temperature exhaust gas stream 127and is axially released into an exhaust system (not shown).

The compressor housing 107 and compressor wheel 113 form a compressorstage. The compressor wheel, being driven in rotation by the exhaust-gasdriven turbine wheel 111, is configured to compress axially receivedinput air (e.g., ambient air 131, or already-pressurized air from aprevious-stage in a multi-stage compressor) into a pressurized airstream 133 that is ejected circumferentially from the compressor. Due tothe compression process, the pressurized air stream is characterized byan increased temperature over that of the input air.

Optionally, the pressurized air stream may be channeled through aconvectively cooled charge air cooler 135 configured to dissipate heatfrom the pressurized air stream, increasing its density. The resultingcooled and pressurized output air stream 137 is channeled into an intakemanifold 139 on the internal combustion engine, or alternatively, into asubsequent-stage, in-series compressor. The operation of the system iscontrolled by an ECU 151 (engine control unit) that connects to theremainder of the system via communication connections.

Turbine

With reference to FIGS. 1 and 2, the turbine housing 105 forms anexhaust gas entrance passageway 217 leading into a primary-scrollpassageway 219 configured to receive the exhaust gas stream from theengine in a direction normal to and radially offset from the rotor groupaxis of rotation 103. The primary-scroll passageway substantially formsa convergent passageway that spirals inward enough and converges enoughto accelerate the exhaust gas 223, funneling it to impinge on theaxially upstream end 275 of turbocharger turbine blades 231, and thenpassing through gaps between the blades.

At the location where the exhaust gas entrance passageway 217 leads intothe primary-scroll passageway 219, there is a structure that ischaracterized by a tongue-like shape when viewed in the cross-section ofFIG. 2 (i.e., taken normal to the rotor group axis of rotation 103).More particularly, the structure of a tongue 235 appears as a protrusionhaving a tip.

It is desirable for typical automotive turbochargers to have on theorder of eleven turbine blades 231, and often have a radius between 12mm and 75 mm. Within the typical eleven-blade automotive turbine, and attypical automotive turbine rotational rates, the blades pass the tongue235 at a frequency that is within the human audible range. This createsa humming noise that is not desirable.

Under a first embodiment of the invention, the turbine wheel 111, whichis part of the rotor group, is characterized by a line defining the axisof rotation 103 (i.e., the axis is collinear with the line). The turbinewheel may include a rotationally symmetric hub 241 (possibly beingcharacterized by spherical symmetry around the axis of rotor rotation).The turbine hub supports the plurality of blades. The center of mass(“CM”) of the hub is on the axis of rotation, and the CM of theplurality of blades is also on the axis of rotation.

Unlike prior art turbine wheels, the plurality of blades 231 arecircumferentially spaced around the hub at varying angles such that theblades are rotationally asymmetric around the axis of rotation 103. Forthe purposes of this application, it should be understood that the termrotationally asymmetric is defined to mean that the wheel cannot berotated around the axis of rotation (by any amount other than an integermultiple of 360 degrees) to a position in which the structure issubstantially identical (i.e., identical to within a functionallyreasonable measurement tolerance level).

In this particular embodiment, the turbine wheel 111 consists only ofthe hub 241 and the plurality of blades 231, and the hub is rotationallysymmetric around the rotor group axis of rotation. It should beunderstood that the blades include a fillet that distributes blade rootstresses to the hub.

With reference to FIGS. 1 to 3, to make the blades 231 rotationallyasymmetric, each consecutive pair of blades is characterized by aspacing angle 301 S_(n) between the consecutive pair of blades. Thespacing angle may be measured from any reference point (i.e., any axial,radial and circumferential position) on the consecutive blades so longas it is consistently done from the same reference point on each blade.For example, it could be measured from the leading edge of the bladewhere the leading edge connects to the hub on each blade. Alternatively,it could be measured from the CM of each blade, which might simplifycalculation of the CM of the complete set of blades. The spacing anglesS_(n) do not vary periodically in a pattern that would create rotationalsymmetry.

The calculation of the set of spacing angles 301 that avoids rotationalsymmetry of the wheel 111 (and more particularly of the blades 231), andyet that has the CM on the rotor group axis of rotation 103, is acomplex mathematical problem. The problem can be substantiallysimplified by allowing for the spacing of the blades to have a plane ofsymmetry. More particularly, the turbine wheel (and more particularlythe plurality of turbine blades) is characterized by a second line 303that is normal to and intersecting with the line defining the axis ofrotor rotation 103. The axis of rotation and the second line define aplane of symmetry by extending along and being contained within theplane, and the spacing angles of the plurality of blades are symmetricacross the plane of symmetry (i.e., they are mirrored, as indicated inFIG. 3). In the case where a spacing angle extends across the plane ofsymmetry, it is bisected by the plane so that half of the spacing angleis on each side of the plane.

As was previously noted, a prior art solution to this problem was toincrease the number of blades to a point at which the hum frequency isout of the human range of hearing (e.g., greater than 20,000 Hz). One ofthe downsides of this solution is that the blade crowding limited thesize of the fillets, and therefore limited the spreading of blade rootstresses. Therefore, the blade spacing angles 301 S_(n) are preferablylimited to at least the minimum size of the blade spacing between evenlyspaced blades for the fewest number of blades necessary to take the humout of the range of human hearing (e.g., 13), and possibly larger number(e.g., 18) as long as the blade root stresses are within acceptablelevel. As was hinted at above, the problem of finding good series ofblade spacing angles 301 is a difficult optimization problem. Thisproblem may be solved by using an iterative computerized softwaresystem. The system will be programmed to implement a method of designingand creating turbine wheel tooling for creating a turbine wheel having nasymmetrically spaced blades and an axis of rotation.

With reference to FIGS. 3 to 5, steps are identified to provide a methodof designing and creating turbocharger wheel tooling for creating aturbocharger wheel having n blades asymmetrically spaced and an axis ofrotation. A number of blades and an initial spacing angle S_(IN) foreach consecutive pair of blades must first be established 401. Thenumber of blades will typically be selected by a design team based onthe desired parameters of the turbine, such as the anticipated operatingspeeds of the turbine and aerodynamic considerations. The initialspacing angles can be set in a variety of ways. For example, the averagespacing angle could be randomly varied, or the design team couldarbitrarily select numbers. Typically, it would be desirable to useinitial spacing angle 301 values that vary significantly from one bladespacing angle to the next. An exception to this would be for wheels withan odd number of blades and a plane of symmetry on the line between twoconsecutive spacing angles, wherein the spacing angles on immediateopposite sides of the plane will inherently be the same.

Next, an iterative optimization computer program is run 403 on acomputer. The program is configured to solve a constrained optimizationproblem using the steps of (1) calculating 405 a CM 501 of either thecomplete set of blades 231 or of the entire wheel 111 (i.e., a CMindicative of the CM of the blades with respect to the axis of rotorrotation); (2) iteratively adjusting 407 the spacing angles such thatthe distance between the calculated center of mass and the wheel axis ofrotation is decreased and the spacing angles vary according to a set ofone or more constraints and an objective variable in order to limit theacoustic energy generated at any one frequency audible to humans; and(3) continuing the iterations 409 until the calculated CM is effectivelyon the axis of rotation and the variation of consecutive spacing anglesis optimized to establish a set of final spacing angles S_(F) inconsecutive order. Greater detail of the optimization computer programis not necessary, as the field of programming computers to iterativelyoptimize variables is known.

The distance between the calculated center of mass and the wheel axis ofrotation is a relatively straight forward calculation. Nevertheless, avariety of different constraints and/or objective variables might beused to limit the acoustic energy generated at any one frequency. Eachset of one or more constraints and an objective variable will havestrengths and weaknesses, such as required computation time and/oraccuracy in representing an optimal acoustic solution. Such constraintsand objective variables might include comparisons of consecutive bladeangles, and comparisons of all blade angles to one another, among otheroptions.

As an example of the first type of constraint and objective variabledescribed above, an objective variable that might be used is to maximizethe variation of each consecutive blade angle, while the blade anglesare constrained to be within a minimum and a maximum angle. As anexample of the second type of constraint and objective variabledescribed above, the standard deviation of the set of all blade anglescould be maximized, while the blade angles are constrained between aminimum and a maximum angle.

For the purposes of this application, the variation of consecutivespacing angles is considered to be optimized when the optimizationcomputer program iteratively reaches an optimum level on the objectivevariable (e.g., the variation of each consecutive pair of blade anglesis maximized). It should be noted that optimized spacing angles may bedifferent when different constraints and/or objective angles are used.Other objective variables that might be used include: target standarddeviation level (rather than maximum), target angle variation (ratherthan maximum), angle variations within a certain range, and the like.

The step of iteratively adjusting 407 the spacing angles is preferablydone by increasing the variation of consecutive spacing angles. Itshould be noted that a variety of techniques may be used to establish alevel of the variation of consecutive spacing angles. For example, thesum of the absolute value of the difference between each consecutivepair of spacing angles may be calculated. The larger this number is, thegreater variation there is considered to be between all such consecutivespacing angles.

It should be noted that during the iterations of the solution, the CMwill not be restricted to the plane of symmetry unless the spacing angleis considered to be the spacing between the CM of each blade.

Once the optimization program has established a set of final spacingangles S_(F) in consecutive order, tooling is formed 411. The tooling isconfigured to create a void usable for creating turbine wheelscharacterized by having the set of final spacing angles S_(F) angles inconsecutive order.

As was discussed above, the optimization problem is simplified when theblade spacing angles are symmetric across a plane of symmetry. Toimplement that, in the step of establishing 401 initial spacing angles,the initial spacing angles S_(IN) are selected to be symmetric 421across a plane of symmetry that contains and is defined in part the linedefining the axis of rotation. Additionally, in the step of running 403an iterative optimization computer program, the iterative adjustment ofthe spacing angles maintains 423 the symmetry of the spacing anglesacross the plane of symmetry. Advantageously, this reduces the number ofvariables.

As was previously discussed, it is preferable to set a minimum spacingangle that allows for good mechanical and aerodynamic characteristics.Thus, in the step of iteratively adjusting the spacing angles, eachspacing angle is constrained to be greater than a minimum spacing angleS_(MIN), such as 20.0 or 27.7 degrees (corresponding to the spacing of18 or 13 blade evenly spaced blades).

With reference to FIGS. 6 and 7, it should be noted that thecalculation-simplifying procedure of using a plane of symmetry can beimplemented for either an even number of blades or an odd number ofblades. To provide for an odd number of blades, the reference point of afirst blade 601 is considered to be on the plane of symmetry 303, and anopposing spacing angle 603 on the opposite side of the wheel is bisectedby the plane of symmetry, as is shown in FIG. 6. One side effect of thisis to have two adjoining blade spacing angles that are the same (oneither side of the first blade). To provide for an even number ofblades, no blade reference points are considered to be on the plane ofsymmetry, and two opposing spacing angles 701 on opposite sides of thewheel are each bisected by the plane of symmetry, as are shown in FIG.7. In either case, it is not required to use one of the bisected anglesfor the purposes of CM calculation, though it is preferable to use itfor spacing angle variation calculations.

It is to be understood that the invention comprises apparatus andmethods for designing and for producing a turbine blade, as well as theapparatus of the turbine blade itself. Alternate variations of theseembodiments could comprise other types of blade configurations.Moreover, while this invention is described for a turbine wheel,compressor wheels may also be within the scope of the invention,although there might be greater risk of flow instability issues. Inshort, the above disclosed features can be combined in a wide variety ofconfigurations within the anticipated scope of the invention.

While particular forms of the invention have been illustrated anddescribed, it will be apparent that various modifications can be madewithout departing from the spirit and scope of the invention. Thus,although the invention has been described in detail with reference onlyto the preferred embodiments, those having ordinary skill in the artwill appreciate that various modifications can be made without departingfrom the scope of the invention. Accordingly, the invention is notintended to be limited by the above discussion, and is defined withreference to the following claims.

What is claimed is:
 1. A turbocharger wheel for use with a rotor group, comprising: a hub; and a plurality of blades; wherein the turbocharger wheel is characterized by an axis of rotation; wherein the center of mass of the hub is on the axis of rotation; wherein the center of mass of the plurality of blades is on the axis of rotation; and wherein the plurality of blades is circumferentially spaced around the hub such that the plurality of blades are rotationally asymmetric around the axis of rotation.
 2. The turbocharger wheel of claim 1, wherein the wheel consists only of the hub and the plurality of blades, and wherein the hub is rotationally symmetric.
 3. The turbocharger wheel of claim 1, wherein: each consecutive pair of blades of the plurality of blades is characterized by a spacing angle between the consecutive pair of blades; a plane of symmetry is defined in part by the axis of rotation, which extends along the plane of symmetry; and the spacing angles of the plurality of blades are symmetric across the plane of symmetry.
 4. The turbocharger wheel of claim 1, wherein the wheel has a radius between 12 mm and 75 mm.
 5. The turbocharger wheel of claim 4, wherein: each consecutive pair of blades is characterized by a spacing angle between the consecutive pair of blades; and each spacing angle is greater than 20.0 degrees.
 6. The turbocharger wheel of claim 1, wherein: each consecutive pair of blades is characterized by a spacing angle between the consecutive pair of blades; and each spacing angle is greater than 20.0 degrees.
 7. A method of designing and creating turbocharger wheel tooling for creating a turbocharger wheel having n blades and an axis of rotation, comprising: establishing an initial spacing angle S_(IN) for each consecutive pair of blades; running an iterative optimization computer program on a computer, the program being configured to solve an optimization problem using the steps of calculating a center of mass indicative of the center of mass of the plurality of blades with respect to the axis of rotation, iteratively adjusting the spacing angles such that the distance between the calculated center of mass and the wheel axis of rotor rotation is decreased and the spacing angles vary enough to limit the acoustic energy generated at any one frequency audible to humans, and continuing the iterations until the calculated center of mass is effectively on the axis of rotation and the variation of spacing angles is optimized to establish a set of final spacing angles S_(F) in consecutive order; and once the optimization program has established a set of final spacing angles S_(F), forming tooling that is configured to create a void usable for creating turbocharger wheels characterized by having the set of final spacing angles S_(F) in consecutive order.
 8. The method of claim 7, wherein, in the step of continuing the iterations, the spacing angles are iteratively adjusted such that the variation of consecutive spacing angles is optimized.
 9. The method of claim 7, wherein: in the step of establishing, the initial spacing angles S_(IN) are selected to be symmetric across a plane of symmetry that is defined in part by the axis of rotation, which extends along the plane of symmetry; and in the step of running an iterative optimization computer program, the iterative adjustment of the spacing angles maintains the symmetry of the spacing angles across the plane of symmetry.
 10. The method of claim 9, wherein, in the step of continuing the iterations, the spacing angles are iteratively adjusted such that the variation of consecutive spacing angles is optimized.
 11. The method of claim 7, wherein each spacing angle is constrained to be greater than a minimum spacing angle S_(MIN).
 12. The method of claim 11, wherein the minimum spacing angle S_(MIN.) is 20.0 degrees. 